A conventional charging system may only be able to charge an energy storage device of a predetermined type, and may not be able to detect a voltage of the energy storage device and determine, in response to the detected voltage, an operating state (e.g., a charging state, a standby state or a discharging state) of the energy storage device. When energy storage devices of different types are to be charged, multiple conventional charging systems dedicated to respectively charge these energy storage devices must be used.